The present invention relates generally to a vehicle seat having an inflatable airbag contained therein and in particular to a trim cover for the seat having a reinforced region adjacent the airbag with a weakened zone forming a tear line for deployment of the airbag through the trim cover.
Generally, seat mounted airbag systems fall into two different categories known as class A and class B. A class A airbag deploys from a visible, discreet door in the seat. A class B airbag is disposed beneath the seat trim cover and is designed to deploy through the trim cover without the use of a visible door. An advantage of a class A airbag with the visible door is that deployment of the airbag through the door uses technology that has already been developed for front crash airbags mounted in steering wheels and instrument panels. The technology for providing consistent and repeatable deployment of the airbag through such a door is well developed. A class B airbag is often preferred for styling considerations. A disadvantage of a class A airbag is that the airbag location in the seat is generally limited to the side or rear of the seat so that the visible door is not part of the seating surface engaged by a seat occupant. If it is desired for an airbag to deploy through a front corner of the seat back, such as the bolster area, it may not be possible to use a class A airbag since the door may interfere with the seating surface of the seat. Rather, class B airbag must be used in which the airbag is underneath the seat trim cover and typically covered by a foam pad so that it does not adversely impact the seat comfort. However, with a class B airbag, there are considerably more variables involved with providing consistent airbag deployment and in meeting the desired airbag in-position timing.
The seat trim cover provides numerous variables effecting airbag deployment. The trim cover type, such as cloth, vinyl, leather, etc., and combinations of these various types all behave differently and have different tensile and tear strength. In addition, different materials of the same types such as different woven fabrics have different tensile strengths, tear strengths, weave nap direction, etc. which can effect the manner in which an airbag deploys through the trim cover if the airbag deploys by rupturing the trim cover. Other variables introduced by the trim cover include the strength of the trim cover scrim layer or backing, and the strength of the thin layer of foam that is typically laminated to the underside of the trim cover outer layer.
Wear of the trim cover material over time and damage to the trim cover by cutting, puncturing, cigarette burns, etc., also introduces variables in airbag deployment. For example, a cut in the trim cover at a location other than the intended deployment location can cause the trim cover to rupture at the wrong location, resulting in the airbag being out of position or taking more time to reach its position.
One approach to reduce some of the variables caused when deploying an airbag through the trim cover is to deploy the airbag through a seam in the cover rather than rupturing the cover material itself. While seam deployment reduces variability, it limits seat styling by dictating where the seam is located.
It is an object of the present invention to provide a trim cover for a vehicle seat with an airbag in which the airbag deploys by rupturing the trim cover by reducing the variability in trim cover rupture to achieve a consistent and predictable airbag deployment.
To accomplish the above, the trim cover employs a reinforcement in the region of the trim cover overlying the inflatable airbag. The reinforced region has a weakened zone forming a tear line for directing deployment of the airbag through a predetermined location in the trim cover. By reinforcing the trim cover in the region overlying the airbag and surrounding the weakened zone, the trim cover is shielded or protected from the inflation forces except for the weakened zone forming the tear line. This tear line thus becomes the "weak link" in the trim cover, resulting in the trim cover rupturing at the tear seam as oppose to other nearby locations.
In a preferred embodiment of the invention, the trim cover is reinforced by the provision of a layer of sheet material to the inner side of the trim cover forming a reinforcing panel. The reinforcing panel has a higher strength and is less stretchable than the outer surface layer of the trim cover. Preferably, the reinforcing panel is a low strength material compared to the outer layer. A known material for this application is the same material used in the airbag which naturally must withstand the airbag inflation forces without failure. Other high strength sheet materials may be used as well. Preferably, the reinforcing panel is laminated to the trim cover material. The reinforcing panel is cut along a line which may be straight or of irregular shape to provide the weakened zone in the trim cover.
In a typical construction, the trim cover material has an outer surface layer and a thin layer of foam. The reinforcing panel layer is positioned on the inner surface of the foam layer. The tear line is preferably formed by cutting both the reinforcing panel and through the foam layer. One method of manufacturing the trim cover is to first laminate the outer layer, foam and reinforcing panel to one another and then laser cut the reinforcing panel and the foam layer along the tear line. Depending on the particular application, the laser cut may partially penetrate into outer layer material itself. Alternatively, the cut may only partially penetrate through the foam or may only penetrate through the reinforcing layer. In another alternative, the laser cut may penetrate partially into the outer layer, weakening it as well.
In the preferred embodiment, the layers of the trim cover are laminated together and then laser cut to form the weakened zone. It is possible to precut the various layers and then join them together with the cut lines aligned with one another. As an alternative, the reinforcing panel may be joined to the other layers only at the perimeter of the reinforcing panel.
The function of the reinforcing layer is to strengthen and reduce the stretch of the trim cover in the region surrounding the tear line. A high strength and low stretchable material such as airbag fabric will perform this function. However, the same function may be achieved with a reinforcing material that is merely less stretchable than the outer layer material. Such a material, when cut to form the weakened zone and laminated to the outer layer, will result in the outer layer stretching more at the tear line than the surrounding area. Thus the outer layer will fail at the tear line when the airbag deploys. Furthermore, the reinforcing layer may not need to be high strength material. As long as the combination of the reinforcing layer and the outer layer is stronger than the outer layer by itself, the combined layers with the weakened zone in the reinforcing layer will result in failure at the tear line created by the weakened zone in the reinforcing layer.
Further objects, features and advantages of the invention will become apparent from a consideration of the following description and the appended claims when taken in connection with the accompanying drawings.